Dental composites made from organic resins and fillers are finding increasing use in dental applications, especially in restorative dentistry, due to their excellent aesthetic properties. Typical dental composite resins contain low viscosity di(meth)acrylate monomers, which serve as diluents that facilitate high filler levels. These diluents usually are small molecular weight (meth)acrylates, such as triethyleneglycol dimethacrylate (TEGDMA), which shrink substantially upon polymerization due to their low molecular weight. Polymerization shrinkage can lead to a number of problems in dental applications. For example, it often causes gaps between the composite and the tooth structure, which can lead to post-operative sensitivity, microleakage, enamel edge cracks, and secondary caries.
A number of factors are believed to play a role in polymerization shrinkage. It has been postulated that shrinkages occur as the van der Waals distance between monomers are replaced by covalent bonds and the packing density of the polymers increases in comparison to that of the monomers. Recent efforts have been made to reduce polymeric shrinkage by attempting to minimize such phenomena; however, many of the low-shrink compositions currently available lack the physical, mechanical, and optical properties required for dental applications. Moreover, not all low-shrink compositions are efficiently polymerizable under conditions that are suitable for use in the oral cavity. Thus, despite substantial advancement in this area, polymerization shrinkage remains a significant problem when working with certain types of dental composites. Consequently, there remains a need for new composite materials that exhibit reduced polymeric shrinkage without sacrificing other beneficial properties, such as fracture toughness and aesthetics.